The invention relates to a water-continuous system and a method of polymerization.
In the prior art water-continuous systems of polymerizable aromatic oils are known which are used for coating surfaces. Thus DE OS 42 29 192 A1 shows a shaped glass part with an antistatic coating which was chemically produced with thiophene derivatives, like 3,4-ethylenedioxythiophene (EDT) from a dilute aqueous solution of the monomers by using polystyrene sulfonic acid as solvating agent. More concentrated water-continuous systems are presented in U.S. Pat. No. 5,575,898. Wolf et al. discloses a process for through-hole plating with microemulsions containing 3,4-substituted thiophenes up to 9%. The microemulsions are formed by diluting with water up to 10% of a concentrate comprising a surfactant and up to 90% of the thiophene derivatives. The maximum concentration of the thiophene derivatives in a microemulsion used for the polymerization by an oxidizing agent is disclosed in EXAMPLE 3 of U.S. Pat. No. 5,575,898. A microemulsion with 1.2% of 3,4-ethylenedioxythiophene was used for the deposition of the polymer on a printed circuit board which had been treated with potassium permanganate. The documents FR 2,698,379, FR 2,698,380 and EP 695,794 demonstrate the electrochemical polymerization of pyrrol and pyrrol derivatives.
The processes known from the prior art for the coating from water-continuous systems, however, have some disadvantages. The rate of deposition for the coating by electrochemical polymerization is very low for those processes. Very high potentials must be chosen for the deposition yielding a reduced quality of the products. Furthermore, the layer thickness of the polymer coating is difficult to regulate yielding less controlled products with respect to the thickness of coating. The consumed monomer must be replaced by dosing and poorly dissolves in diluted water-continuous systems. For that reason coating cannot be performed in a continuous process from water-continuous systems according to the prior art.
Therefore, it is the objective of the invention to provide a water-continuous system, which exhibits a high deposition rate and a low deposition potential during the electrochemical polymerization, and further enables a good control and regulation of the thickness of the coating during the chemical polymerization. Moreover, the coating shall be practicable in a continuous process.
With the water-continuous system of the invention, it is possible now to coat surfaces in a continuous process with high rates of deposition and under control of the development of the layer thickness. Using liquid crystalline systems, the generation of layers of defined thickness is possible. It is controlled by the conditions of deposition. For the electrochemical polymerization, it is possible to work with lower deposition potentials. A better quality of the layer is obtained.
The invention will become apparent in greater detail from the description of examples on the basis of the accompanying drawings.